Persons with HIV often have significant mental health and substance use problems. Research is needed to learn more about access and barriers to appropriate mental health services for this population, and to understand the consequences of these mental health problems for quality of life, use and costs of HIV medical care, and adherence to new and effective HIV medications. Such research can inform efforts to improve services for persons with HIV and mental health problems. The proposed study would contribute to research knowledge of these issues by conducting analyses of data collected as part of the HIV Cost and Service Utilization Study (HCSUS). HCSUS is the first study of a national probability sample of adults with HIV. The data available to date include a baseline and 2 follow-up surveys, a supplemental mental health survey, and ancillary medical and financial information collected from a cohort that was sampled and recruited to the study in 1996 (N=2864). The work proposed here represents a continuation of effort by members of the original study's mental health research team, and has the following specific aims: 1) To investigate how changes in treatment of HIV and physical well-being affect mental health symptoms and use of services; 2) To investigate factors related to access to mental health and substance abuse care for special populations with HIV, including minorities and women; 3) To determine the impact of mental health symptoms and substance use on general medical costs among patients with HIV; 4) To examine the impact of mental health symptoms and substance use on adherence to antiretroviral medications for HIV, and to investigate the reasons for poor adherence; 5) To investigate the temporal association between health-related quality of life and mental health, and the extent to which social support and coping mediate the association.